Convective heat transfer enhancement versus disenhancement: Impact of fluid-mover characteristics

Abstract

Methods of enhancing heat transfer rates have primarily been based on geometrical modifications and supplementations of basic heat transfer devices. To evaluate the extent of the enhancement (or of a possible disenhancement), it has been traditional to compare the heat transfer performance of the basic and the enhanced devices under certain constraints. Seemingly, the most popular among the constraints is that both the compared devices be operated at the same pumping power. Other popular conditions of constraint include operation at the same pressure drop, mass flow rate, device volume, heat transfer area, temperature difference, and many others. Noteworthy by its absence from consideration as a major factor in affecting the degree of enhancement is the fluid mover that serves to deliver fluid flow to the heat transfer device. The characteristic operating curve of a fluid mover relates its pressure rise to the volumetric flow rate that it provides. The shape of the curve that represents this relationship varies widely among individual fluid movers as well as among different generic types of fluid movers. In the present investigation, the essential role of fluid-mover operating characteristics in affecting heat transfer enhancement is presented and implemented. A case study involving surface geometry enhancement by means of louvered fins is considered along with its unenhanced plain-fin counterpart. For generality, two distinctly different fluid movers are utilized as means of fluid delivery to both the enhanced and unenhanced heat transfer devices. For both of the fluid movers, it was found that the enhanced geometry actually led to a reduction in the rate of heat transfer while giving rise to an increase in pressure drop. It was also shown that enhancement (or disenhancement) depends as much on the characteristics of the fluid mover as it does on the geometry of the heat transfer device in question.